It is common practice for the manufacturer of internal combustion engines to connect each of the assembled engines to a dynamometer through a connecting coupling for various types of testing prior to installing them in vehicles, or preparing them for industrial applications, or shipping them to customers. Such manufacturers occasionally assemble a family of related engine models having different horse power ratings and/or operating characteristics on the same assembly line. As is normally the case, the demand for a particular model fluctuates so that frequently there are more of one or two engine models being assembled than other engine models. When this happens and if the dynamometers and connecting couplings are set up such that they will accept only one engine model, some dynamometers would go unused for lack of particular model builds while stack-up awaiting test would occur at other dynamometers. The problem of having to couple a particular engine model to a particular dynamometer is compounded when, depending on its use, the same engine model may be tested without a flywheel or it may be tested with one of several flywheel designs mounted on the crankshaft. To stock a complete coupling for every engine variation at every dynamometer is not economically practical.
A basic design problem encountered in the design of a coupling for connecting an engine to a dynamometer is that of avoiding damaging resonant loads. For example, the resonant torque values are frequently approximately 8 times the normal engine lug torque and many of the presently available couplings have a resonant life of only 5 minutes. The resonant loads also create problems in the mechanical connection between the coupling and the dynamometer shaft. An experimental coupling which is utilized in the manufacturing facility of the Assignee of the present invention and which led to the coupling design of the present invention employed a conventional key and key-way drive connection between the coupling and the dynamometer shaft. However, the resonant torque loads passing through the key and key-way caused deterioration thereof and led to replacement of the key and repairs to the shaft and mating elements of the coupling.